The present invention is directed to a water-absorbent pressure sensitive adhesive.
There is an ongoing need in the medical industry for a pressure sensitive adhesive for long-term skin applications. An adhesive possessing this quality would be ideal for applications in which a patient's skin is wetted as a result of either site preparation or the accumulation of moisture under the adhesive during normal perspiration. This type of system could readily be used for surgical drapes, wound dressings, or other special applications in which durable bonding to fully saturated skin tissue is needed. There has yet to be an effective adhesive product to meet these demanding needs.
To meet the criteria described above, an adhesive must possess certain inherent qualities that are related to the chemistry of the adhesive. The design of such an adhesive should include a balance of moisture absorbent capabilities and adequate pressure sensitive adhesive properties. First, hydrophilic character will enable the adhesive to interact with moisture and free up bonding sites at the adhesive/skin interface. Advantageously, not only will such an adhesive system readily absorb moisture at the skin-adhesive interface, but the adhesive will also serve as an effective vehicle to transport absorbed moisture in the form of water vapor from the adhesive to the ambient environment. This will allow for intimate contact of the adhesive with the skin. Secondly, hydrophobic character will enable the adhesive to exhibit the mechanical properties needed for initial, and durable, bonding to skin. Reactive monomers--in which the homopolymers have thermal glass transition temperatures that are well below ambient--usually possess the tack required for pressure sensitive adhesive bonding. Subsequent cross linking may provide the required durability needed for long term wear.
Consideration must also be given to the safety of the adhesive. The adhesive must be non-toxic if it is to be used for medical purposes. This is especially true when bond sites are near open wounds or abrasions. An ideal long-term wound care adhesive should contain no extractables such as unreacted monomers, additives, or soluble polymeric systems. Such extractables could break down when exposed to solvents such as water. Absorption into skin, or migration to the open wound, may produce harmful effects to the patient. Therefore, it is important for the adhesive to maintain chemical integrity throughout its use.
The mechanical properties of a desirable long-term skin or wound-care adhesive are intimately related to its composition. An ideal candidate must maintain an aggressive adhesive nature throughout its use. This includes not only the short term needs of the consumer, but the adhesive must be durable after long-term storage. In ambient environments, an adhesive might see a wide range of temperature cycles over extended periods of time. Subsequent chemical changes caused by reactions, such as further crosslinking or degradation, may weaken the pressure-sensitive qualities of the adhesive system.